Charged particle beam apparatus

ABSTRACT

A charged particle beam apparatus that can achieve both high defect-detection sensitivity and high inspection speed for a sample with various properties in a multi-beam type semiconductor inspection apparatus. The allocation of the primary beam on the sample is made changeable, and furthermore, the beam allocation for performing the inspection at the optimum inspection specifications and at high speed is selected based on the property of the sample. In addition, many optical parameters and apparatus parameters are optimized. Furthermore, the properties of the selected primary beam are measured and adjusted.

CLAIM OF PRIORITY

The present application claims priority from Japanese application JP2007-052166 filed on Mar. 2, 2007, the content of which is herebyincorporated by reference into this application.

FIELD OF THE INVENTION

The present invention relates to an inspection apparatus and ameasurement apparatus that are employed in a semiconductor process, moreparticularly, to a high speed and high precision charged particle beamapparatus.

BACKGROUND OF THE INVENTION

In the semiconductor process, a charged beam (hereinafter, referred toas primary beam) such as an electron beam or an ion beam is irradiatedon a sample, and signals from a generated secondary charged beam(hereinafter, referred to as secondary beam) such as a secondaryelectron beam are acquired, wherein an electron beam length measurementapparatus that measures the shape and size of a pattern formed on thesample, and an electron beam inspection apparatus that inspect theexistence or nonexistence of defects on the sample are employed.

In such a charged particle beam apparatus, enhancing the speed toprocess the sample, that is, enhancing the speed to inspect the sampleis an important problem together with the enhancing the sensitivity todetect defects on the sample. In order to solve this problem, amulti-beam type charged particle beam apparatus in which plural beams isemployed has been proposed. For example, in Japanese Patent ApplicationNo. 2006-144934, a multi-beam type charged particle beam apparatus isdisclosed, wherein an electron beam emitted from a single electron gunis separated into plural beams, and the plurality of beams, which areformed individually by focusing lenses arranged like an array, areprojected and scanned on the sample using a single optical element.

SUMMARY OF THE INVENTION

As mentioned above, by using the multi-beam type charged particle beamapparatus in which plural primary beams are scanned on the sample usinga single optical element, for example, to study the shape and theexistence or nonexistence of defects of a semiconductor or a similarobject, a problem that arises is the reduction of the size of theprimary beam (beam diameter) to scan the sample. Also in the multi-beamtype charged particle beam apparatus, as in the single beam typeelectron beam inspection apparatus, when the aperture angle and thecurrent density of the primary beam is increased to enhance theinspection speed, the aberrations of lenses and the beam blurring owingto the Coulomb repulsive force increase, resulting in reducing theinspection sensitivity. In addition, in the multi-beam type chargedparticle beam apparatus, the off-axis aberrations, which are caused whenthe primary beam runs along the trajectory that is away from the centerof optical elements such as lenses, should be taken into account.

Another problem is to detect the secondary electron beams that areemitted from the sample by irradiating it with the plurality of beams.If it is possible to separate the secondary electron beams that aregenerated simultaneously at N portions on the sample by scanning Nprimary beams, to make them collide with the corresponding detectors,and to detect them individually, the signals can be acquired with highS/N ratios. On the contrary, if it is not possible to separate thesecondary electron beams that are generated simultaneously at N portionson the sample, some parts of the secondary electron beams will collidewith wrong detectors, which will worsen the S/N ratios. Therefore, it isnecessary to control the secondary beam optical system so that thesecondary beams emitted from plural portions on the sample aredistributed separately with each other on the detectors.

These two problems and the relationship with the allocation of theprimary beam will be explained in detail. From the viewpoint of theprimary beam diameter, In order to decrease the off-axis aberrations, itis more advantageous to place the primary beam irradiated on the samplecloser to the central axis. On the other hand, by placing the primarybeam irradiated on the sample closer to the central axis, the primarybeams get closer with each other, so the intervals among the positionsof the secondary beam generation on the sample become narrower.Consequently, it becomes difficult to control the secondary beam opticalsystem to distribute the secondary beam separately with each other onthe detector, resulting in decreasing the degree of separability of thesecondary beams (the fraction of the secondary beams that are detectedby the specified detectors among all the secondary beams generated bythe irradiation of the same primary beam). As mentioned above, twoproblems of decreasing the beam diameter of the primary beam andseparately detecting the secondary beams are in the relationship oftrade-off.

On the other hand, in the semiconductor process, the property of waferis different for each product class, process, and lot; and theprocessing conditions for carrying out the high precision processingalso vary for each case. For example, in the semiconductor inspectionapparatus, the inspection specifications for obtaining a highsensitivity in detecting defects change by the property of the wafersample. Here, the inspection specifications represent the inspectionmethod or the inspection conditions that directly determine the effectof the inspection. For example, according to the material and thicknessof the film to form a pattern, and the structure of the pattern,optimizing the measurement conditions such as the size of the primarybeam (beam diameter) to scan the sample and the energy of the primarybeam when it is entered on the sample are effective for obtaining a highsensitivity in detecting defects. In addition, the optimum inspectionspecifications depend on what kind of defect is to be detected. Forexample, to detect electrical defects, it is necessary to adjust thecurrent density of the primary beam that enters in the sample and theelectric field on the sample surface to make a desired charged state.Conversely, in detecting the pattern shape defects, the beam diameterinfluences the sensitivity in detecting the defects rather than thecharged state of the sample surface.

The purpose of the present invention is to provide a charged particlebeam apparatus that can process the sample with various properties asmentioned above at high precision and high speed.

In order to accomplish the above-mentioned purpose, for the firstembodiment of the present invention, in the multi-beam typesemiconductor inspection apparatus, the allocation of the primary beamon the sample is made changeable, and furthermore, the beam allocationfor carrying out the inspection of the sample with the optimuminspection specification at high speed is selected. Also, the propertyof the selected primary beam is measured and adjusted. In addition, inanother embodiment of the present invention, not only the beamallocation but also many optical parameters and instrument parametersare made changeable, and these are optimized.

According to an aspect of the present invention, a charged particle beamapparatus that can achieve both high defect-detection sensitivity andhigh inspection speed can be realized.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing the general configuration of an electronbeam inspection apparatus for explaining the first embodiment of thepresent invention;

FIG. 2A is a diagram explaining the allocation of openings of theaperture lens array;

FIG. 2B is a diagram explaining the beam allocation A;

FIG. 2C is a diagram explaining the beam allocation B;

FIG. 2D is a diagram explaining the beam allocation C;

FIG. 2E is a diagram explaining the beam allocation D;

FIG. 3 is a flowchart explaining the first embodiment of the presentinvention;

FIG. 4A shows an example of an image obtained by a trial inspection;

FIG. 4B is a histogram display of the image brightness;

FIG. 5 is a flowchart explaining the second embodiment of the presentinvention; and

FIG. 6 is a window showing the results of the optical adjustment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, the present invention will be explained in detail bydescribing some preferred embodiments of the invention with reference tothe accompanying drawings. In addition, for all the drawings to describethe embodiments of the invention, the same reference numerals are givenfor the same component to abbreviate the repeated explanations.

First Embodiment

FIG. 1 shows a skeleton framework of the multi-beam type semiconductorinspection apparatus related to the first embodiment of the presentinvention. The electron optical system of this apparatus is divided intoa primary optical system controlling the primary beam that is emittedfrom a cathode 101 and reached to a sample 116, and a secondary opticalsystem controlling the secondary beam that is generated by theinteraction of the primary electron beam and the sample. The chain linerepresents an axis that should coincides with the symmetric axis of theroughly rotational-symmetrically formed optical system; in short, thisaxis is considered to be the mechanical central axis of the chargedparticle beam optical axis. This axis becomes a basis of the primaryelectron beam optical path. Hereinafter, this axis is referred to ascentral axis.

First, configuration of the apparatus is explained. A cathode 101 ismade from a material with a low work function. For the cathode 101, byapplying a high electric potential to an anode 104, an acceleratingelectric field is formed between the cathode 101 and the anode 104. Anelectromagnetic lens 103 superimposes a magnetic field on thisaccelerating electric field. In the downstream of the anode 104, acondenser lens 106, an aperture array 107 in which plural apertures isarranged on the same board, a beam selection aperture 108 and a beamselection stage 109 on which the beam selection aperture is mounted andmoved, a lens array 110 with plural apertures, a Wien filter 111,objective lenses 112 a and 112 b, a deflector 113, a ground electrode114, and a surface electric field control electrode 115 are allocated,composing the primary optical system. As is not shown in the figure, inthe primary optical system, a current limiting aperture, an aligner foradjusting the central axis (optical axis) of the primary beam, and otherdevices are allocated.

The stage 117 moves with a wafer 116 mounted on it. A negative electricpotential (hereinafter, referred to as retarding electric potential) isapplied to the wafer 116. As is not shown in the figure, a wafer holderexists between the wafer 116 and the stage 117 in the electricallyconducted state with the wafer; and by connecting a retarding powersupply 118 to this wafer holder, a desired voltage is applied to thewafer holder and the wafer 116. On the stage 117, a reference sample 132that is used for adjusting the electron optical conditions and measuringthe adjusted state, and a Faraday cup 133 that is used for measuring theelectron beam current are provided. As is not shown in the figure, thesystem control section 126 is connected to the Faraday cup 133 throughan amplifier.

The surface electric field control electrode 115, the ground electrode114, the objective lenses 112 a and 112 b, and the Wien filter 111 arealso the parts of the secondary optical system. In the secondary opticalsystem, a secondary beam axis adjustment aligner 121, a secondary beamcondenser lens 122, and other devices are also allocated, playing a roleto make the secondary beam enter in detectors 123 d and 123 f.

The system control section 126 is connected to the detectors 123 d and123 f, and amplifier circuits 124 d and 124 f through an A/D converter125, composing a signal detection system. In addition, two sets ofdetectors and amplifier circuits are shown in FIG. 1; however, in theactual embodiment, plural the sets of detectors and amplifier circuitsare provided according to the number of primary beams that can beformed.

The system control section 126 is a part of the control system thatcontrols the whole apparatus systematically. The control system consistsof the system control section 126, an optical system control circuit127, a selection stage control circuit 128, a scan signal generationcircuit 129, a stage control circuit 130, and other control devices. Thecathode 101, the anode 104, the condenser lens 106, the aperture array107, the Wien filter 111, the objective lenses 112 a and 112 b, theretarding power supply 118, and a surface electric field control powersupply 119 are connected to the system control section 126. In addition,as is not shown in the figure, the secondary beam axis adjustmentaligner 121 and the secondary beam condenser lens 122 are also connectedto the system control section 126 through the optical system controlcircuit 127. The beam selection stage 109 is connected to the systemcontrol section 126 through the selection stage control circuit 128. Thedeflector 113 is connected to the system control section 126 through thescan signal generation circuit 129. The stage 117 is connected to thesystem control section 126 through the stage control circuit 130. Animage display unit 131 is connected to the system control section 126.

The signal detection system is also controlled by the system controlsection. The timing of the signal detection for the detectors 123 d and123 f is determined by a clock signal that the system control section126 generates. That is, the signals of the secondary beam are acquiredsynchronous with the clock signals, and the signal of the secondary beamacquired within one clock interval becomes the brightness signal of theone pixel of an image that is formed by the detected signals. On theother hand, a length that the deflector 113 scans the primary beam onthe sample within one clock interval corresponds to the width of onepixel of the image that is formed by the detected signals.

In addition, as is not shown in the figure, compositional units otherthan the signal detection system, the system control section 126, andeach control circuit are allocated in vacuum chambers, and they are,needless to say, operated after they are evacuated. In addition, a wafertransfer system, which allocates a wafer on the stage from the outsideof vacuum, is, needless to say, provided.

Next, operations and details of the apparatus will be explained. Theprimary beam 102 emitted from the cathode 101 is accelerated in thedirection of the anode 104 while receiving a focusing action by theelectromagnetic lens 103, forming a cathode image 105 (a point at whichthe beam diameter becomes minimum). As is not shown in the figure, anextraction electrode is provided between the cathode 101 and anode 104,as is often seen in a commonly-used electron gun. Also, in the vicinityof the anode 104, an aperture is allocated. By changing the operationconditions of the cathode 101, the extraction electrode, theelectromagnetic lens 103, and the anode 104, it is possible to adjustthe current of the primary beam passing through the aperture and thesize of the cathode image 105. In addition, as is not shown in thefigure, in the downstream side of the anode 104, an aligner to correctthe axis of the primary electron beam is allocated, realizing astructure to enable to correct the axis of the primary beam when it isshifted for the electron optical system in the downstream side. Thecondenser lens 106 aligns the primary beam, whose light source is thecathode image 105, parallel. The aperture array 107 arranges pluralapertures on the same board, and has 9 apertures in the presentembodiment. By unit of the aperture array 107, the primary beam 102 isdivided into 9 primary beams: 102 a, 102 b, 102 c, 102 d, 102 e, 102 f,102 g, 102 h, and 102 j used for inspection. In addition, in FIG. 1, the9 primary beams are drawn as if they are arranged linearly; butactually, they are arranged two dimensionally in a plane perpendicularto the central axis as shown in FIG. 2A. Furthermore, the allocation ofeach primary beam shown in FIG. 2B to FIG. 2E is rotationally symmetric,and the center of the rotational symmetry coincides with the centralaxis in FIG. 1.

The beam selection aperture 108 is a board having plural apertures, andit is mounted on the beam selection stage 109. When the selection stagecontrol circuit 128 is moved by the control of the system controlsection 126, the relative positional relationships between the openingsof the beam selection aperture 108 and the 9 primary beams: 102 a, 102b, 102 c, 102 d, 102 e, 102 f, 102 g, 102 h, and 102 j are adjusted.That is, the position of the beam selection stage 109 is controlled sothat only a desired beam among the 9 primary beams passes through theopening of the beam selection aperture 108, and enters in the opticalsystem in the downstream side. In the present embodiment, the shape ofthe openings of the beam selection aperture 108 and the beam selectionstage is designed 10 so that four different ways of beam allocationsfrom an allocation A as shown in FIG. 2B to an allocation D as shown inFIG. 2E become the candidates. Therefore, one, two, four, or eightprimary beams can enter in the optical system in the downstream side. InFIG. 1, two primary beams 102 d and 102 f are selected, and enter in theoptical system in the downstream side.

Here, the relationship between the allocation of each beam and the beamdiameter of the primary beam will be explained. The allocation of theprimary beam corresponding to the allocation A is the same as the singlebeam; the primary beam is formed on the central axis, and no off-axisaberration is generated. In addition, because the beam currentirradiated on the sample is low, the beam blurring owing to the Coulombrepulsive force is small. Therefore, among the allocations from A to D,the beam diameter of the primary beam on the sample is smallest in theallocation A. On the other hand, in the allocation B, because theprimary beam is formed away from the central axis, the off-axisaberrations are generated, and the total current of the primary beambecomes double; so the beam blurring owing to the Coulomb repulsiveforce becomes larger than that of the allocation A. Therefore, the beamdiameter of the primary beam on the sample is larger than that of theallocation A. In the allocation C, the distance between the primary beamand the central axis is equal to that of the allocation B, the off-axisaberrations are equal to that of the allocation B; however, because thebeam blurring owing to the Coulomb repulsive force becomes larger thanthat of the allocation B, the beam diameter of the primary beam on thesample becomes larger than that of the allocation B. Furthermore, in theallocation D, the distance between the primary beam and the central axisbecomes larger than that of the allocation B and the allocation C, theoff-axis aberrations become larger, and moreover, the beam blurringowing to the Coulomb repulsive force becomes larger than that of theallocation C. Therefore, the beam diameter of the primary beam on thesample becomes largest among the allocations from A to D. On the otherhand, inspection speed is lowest in the allocation A in which the numberof beams is smallest, and the inspection speed becomes higher in theorder of the allocations B, C, D. In addition, the inspection speed canbe expressed by the area of region in which plural primary beams scan inunit time. The measurement speed can be expressed with nearly the samedefinition.

By returning to FIG. 1 again, operations and details of the apparatuswill be explained.

The selected primary beams 102 d and 102 f are focused individually bythe lens array 110. The lens array 110 consists of three sheets ofelectrodes each of which has plural openings; by applying a voltage tothe middle electrode among the three electrodes, this lens array acts asan einzel lens for the primary beams passing through the openings.

The two primary beams 102 d and 102 f focused individually by the lensarray 110 pass through inside the Wien filter 111. The Wien filter 111generates a magnetic field and an electric field, which are at rightangles to each other, in a plane roughly perpendicular to the incidentdirection of the primary beam, and gives a deflection angle for thepassing electron corresponding to the energy. In the present embodiment,the electric field strength and magnetic field strength are set so thatthe primary beam goes straight, and furthermore, for the secondary beamthat enters from the opposite direction, the electric field strength andmagnetic field strength are adjusted and controlled so that thesecondary beam deflects to a desired angle. In addition, for theposition of the Wien filter 111, by taking the effect of aberrations forthe primary beam into account, to reduce the effect, it is allocated tomatch the height of the primary beam that is focused by the lens array110. Components 112 a and 112 b are one set of objective lenses, andboth are electromagnetic lenses. They project the primary beam focusedby the lens array 110 on the sample 116 at a reduced magnification.

The deflector 113 for the scan deflection is made of an electrostaticoctapole, and installed in the objective lens. By the control of thesystem control section 126, the scan signal generation circuit 129generates a signal at a predetermined amplitude and frequency. When thissignal enters in the deflector 113, the primary beam passing throughinside the deflector receives a deflecting action in nearly the samedirection and by nearly the same angle to carry out the raster scanningon the sample, namely, the wafer 116. To the wafer 116, a negativeelectric potential is applied from the retarding power supply 118.Therefore, between this wafer and the ground electrode 114 that isconnected to the ground electric potential, an electric field todeaccelerate the primary beam is formed. The unit 115 is the surfaceelectric field control electrode, and it is a disk like electrode havinga circular opening. The diameter of the opening of the surface electricfield control electrode 115, the distance between the surface electricfield control electrode 115 and the sample 116, and the output voltageof the surface electric field control power supply 119 connected to thesurface electric field control electrode 115 determine the electricfield intensity on the surface of the sample 116.

The surface electric field control power supply 119 is a power supplyconnected to the surface electric field control electrode 115. Theretarding power supply 118 and the surface electric field control powersupply 119 are systematically controlled by the system control section126 through the optical system control circuit 127 as well as otheroptical elements, more specifically, the cathode 101, the anode 104, thecondenser lens 106, the lens array 110, the Wien filter 111, and theobjective lenses 112 a and 112 b.

The stage 117 is controlled by the stage control circuit 130. The systemcontrol section 126 controls the scan signal generation circuit 129 andthe stage control circuit 130 systematically to inspect a predeterminedregion on the wafer 116 one stripe by one stripe that are aligned in thestage driving direction. In addition, in the inspection apparatus of thepresent embodiment, the apparatus is controlled so that the primary beamscans the belt-like regions sequentially by combining the deflectionscan and the stage movement while the stage is moving continuously.

By irradiating the primary beam on the sample, secondary beams such assecondary electron beam and backscattered electron beam are generatedfrom the sample 117. In FIG. 1, the two primary beams 102 d and 102 fare irradiated on the sample; so the secondary beams 120 d and 120 f aregenerated from the two positions on the sample where these primary beamsare irradiated, respectively. The secondary beams 102 d and 102 freceive the focusing actions of the objective lenses 112 a and 112 b,and by the Wien filter 111 that has a deflecting action for thesecondary beams, the trajectories of the secondary beams are separatedfrom the trajectories of the primary beams. After that, the trajectoriesof the secondary beams are corrected by the secondary beam axisadjustment aligner 121, and furthermore, by the focusing action of thesecondary beam condenser lens 122, the secondary beams reach thedetectors 123 d and 123 f, respectively. Signals detected by thedetectors 123 d and 123 f are amplified by the amplifier circuits 124 dand 124 f, digitized by the A/D converter 125, and stored once in amemory device 126 a in the system control section 126 as an image data.After that, an arithmetic section 126 b calculates various statisticsvalues of the image, and finally, a defect judgment section 126 c judgesthe existence or nonexistence of defects based on the predetermineddefect judgment conditions. The judged results are displayed on theimage display unit 131. In addition, when an electron beam apparatus ofthe present embodiment is used for a length measurement SEM, a lengthmeasurement execution section that carries out the length measurementbased on the image pixel data (two-dimensional intensity distributiondata of secondary electrons or backscattered electrons) stored once inthe memory device 126 a is provided instead of the defect judgmentsection 126 c.

Next, the procedure for carrying out the inspection in the presentembodiment will be explained in detail with reference to the flowchartshown in FIG. 3.

When an operator click the Start button displayed on the image displayunit 131 (step 301), the input window is displayed to specify a cassette(not shown in the figure) in which a wafer to inspect is stored. Whenthe operator input the cassette number (step 302), the wafer ID inputwindow is displayed. The operator inputs the lot ID and the wafer ID towhich the wafer to inspect belongs (step 303). Based on these IDs, thesystem control section 126 judges the wafer size and other informationabout the wafer, and mounts the wafer on the stage 117 using the waferloader (not shown in the figure) (step 304).

In step 305, the system control section 126 downloads the information ofthe wafer to inspect such as the product class, the process, thematerial and the thickness of the film to form on the pattern, thepattern shape, and the pattern size (design size) from the server forfactory administration based on the wafer ID. Here, the processrepresents the information on how far the wafer to inspect (or tomeasure) has gone through the manufacturing process of a structuralobject (for example, a semiconductor device or a magnetic head) that isformed on the wafer, and more specifically, it corresponds to theinformation on how far the layer on the wafer has been formed. Inaddition, the pattern represents a pattern (such as wiring or contacthole) of the structural object formed on the wafer. Or, the operator mayinput this information through the wafer information input windowdisplayed on the image display unit 131.

In step 306, the system control section 126 determines the allowablerange of the beam diameter of the primary beam to scan the sample basedon the information that the system control section 126 has downloaded instep 305.

In step 307, the system control section 126 calculates the beam diameterand current of the primary beam on the sample using a formula memorizedbeforehand for all the candidates of the beam allocations. Furthermore,based on the calculated result of the current, the inspection speed isestimated as shown in the table below:

Primary Number of beam Inspection Allocation beams diameter Currentspeed A 1 30 nm  50 nA  25 cm²/h B 2 40 nm 100 nA  50 cm²/h C 4 50 nm200 nA 100 cm²/h D 8 60 nm 400 nA 200 cm²/h

In step 308, the system control section 126 refers to the allowablerange that is determined in step 306, and excludes the candidates of thebeam allocations in which the beam diameter does not satisfy theallowable range. For example, when the pattern size formed on thesample, that is, wafer is large, and if the allowable range of theprimary beam diameter is less than or equal to 60 nm (case I), any beamallocation from the allocation A to the allocation D satisfies theallowable range. However, when the pattern size formed on the wafer issmall, and if the allowable range of the primary beam diameter is 40 nmor equal to 40 nm (case II), the allocation A and the allocation Bsatisfy the allowable range, but the allocation C and the allocation Ddo not satisfy the allowable range, so they are excluded from thecandidates.

In step 309, the system control section 126 selects the beam allocationthat attains highest inspection speed from the candidates that have notbeen excluded in step 308. For example, in case I in which thecandidates of allocations from the allocation A to the allocation Dremain, the allocation D with the highest inspection speed among them isselected. In case II in which only the candidates of allocations of theallocation A and the allocation B remain, the allocation B with thehigher inspection speed between two allocations is selected. Theselected beam allocations are stored in the system control section 126as log data. Also, they may be displayed on the image display unit 131.

In step 310, in order to actualize the beam allocation selected in step309, the system control section 126 moves the beam selection stagethrough the selection stage control circuit 128. More specifically, byadjusting the relative positional relationship between the primary beamsformed by the aperture array and the openings of the beam selectionaperture 108, the openings of the beam selection aperture 108 mounted onthe beam selection stage 109 allow only the predetermined beams to enterthe optical system in the downstream side, and blocks off the remainingbeams.

In step 311, optical adjustment is performed for the primary beams thatenter in the optical system in the downstream side in step 310. By usingthe reference sample 132, the Faraday cup 133, and other devices thatare mounted on the stage 117, the property of the primary beam such asbeam diameter and current are measured for each one of the N primarybeams selected in step 310, and whether or not the beam diameter fallswithin the allowable range is confirmed. If the primary beam isestimated to be shifted for the electron optical system, the shift iscorrected using the aligner (not shown in the figure). After correctingthe shift, the property of the primary beam such as the beam diameterand current are measured again, and the measurement result is displayedon the image display unit 131 for each one of the N primary beams. Inaddition, every optical parameter such as the voltage applied to thealigner, and the measurement results of the beam diameter and currentare stored in the system control section 126 as the log data.

In step 312, the system control section 126 irradiates the primarybeams, which are entered in the optical system in the downstream side instep 310, through the optical system control circuit 127 on the sample116 or the reference sample 132, separates the generated secondarybeams, and adjusts the voltage (or current) applied to the secondarybeam axis adjustment aligner 121, and adjusts the focal length and otherparameters of the secondary beam condenser lens 122 so that thesecondary beams enter in the respective predetermined detectors.Furthermore, the system control section 126 adjusts the gain, offset,and other parameters of the amplifier circuits 124 d and 124 f, andfixes up the waveform of the signals input in the A/D converter 125.

In step 313, the specification window for the alignment is displayed onthe image display unit 131, and when the operator specifies pluralpoints in an alignment chip on the wafer through this window, theapparatus detects the alignment mark automatically, and corrects thestage coordinates for the wafer; that is, the alignment is executed.

In step 314, a trial inspection is performed. Under the opticalconditions for which the apparatus has been adjusted up to the step 313,a trial inspection is carried out for a small region within apredetermined chip. FIG. 4A is an example of a pattern image within thetrial inspection region. Among the patterns arranged like a matrix, thebrightness is different between a normally formed pattern 401 and apoorly formed pattern 402. FIG. 4B shows the histogram display for thebrightness of every pixel in this image. 403 represents a peakcorresponding to the normally formed pattern; and 404 represents a peakcorresponding to the poorly formed pattern.

In step 315, the operator sets a threshold value of the image contrastto use it for judging defects. In the example of FIG. 4A and FIG. 4B, bysetting a threshold value 405 between the peak 403 corresponding to thenormally formed pattern and the peak 404 corresponding to the poorlyformed pattern, it is expected that the defects can be detected with ahigh sensitivity.

After setting the optimum threshold value, the operator clicks theInspect button displayed on the image display unit 131 to start theactual inspection (step 316). The system control section 126 memorizesthe time when the inspection is started, predicts the inspection finishtime based on the inspection speed that is calculated in step 307, anddisplays the inspection finish time on the image display unit 131.

In addition, in the present embodiment, in step 306, the system controlsection 126 determined the allowance range of the beam diameter of theprimary beam to scan the sample; however, when the sample is a productclass with no inspection record such as when the pattern formed on thewafer is newly designed and when a new process is applied to form thepattern, the system control section 126 will not be able toautomatically determine the allowance range of the beam diameter of theprimary beam. In such a case, the operator may input the allowance rangeof the beam diameter of the primary beam to scan the sample through theinspection specification input window displayed on the image displayunit 131.

Furthermore, in the present embodiment, in step 307, the system controlsection 126 calculated the beam diameter and current of the primary beamon the sample by letting the beam allocation as a variable parameter;however, if an aperture array having different sizes of openings ismounted on the movable stage, the aperture half-angle of the beam thatis cut out by the aperture can be variable.

In such a case, the system control section 126 is well to calculate theprimary beam diameter, current, and the inspection speed for all thecombinations of the beam allocations and the beam aperture half-anglesin step 307. For example, if there are four ways in the beamallocations, and three ways of the beam aperture half-angles can betaken, there are 12 ways of combinations; so, the primary beam diameter,current, and the inspection speed are calculated for every combination.Or, it is well to obtain the information by referring to the datameasured beforehand. In step 308, from the 12 ways of combinations, thecandidates of the beam allocations, which do not satisfy the allowablerange of the beam diameter, are excluded from the candidates, and instep 309, it is well to select the combination of the highest inspectionspeed.

Furthermore, in the present embodiment, by using the beam selectionaperture 108 and a beam selection stage 109 on which the beam selectionaperture is mounted, only the predetermined beams were entered in theoptical system in the downstream side, and remaining beams were blockedoff. Or, by using blanking electrodes that act individually on pluralthe charged particle beams, it is also possible to achieve a similaradvantageous effect as the present embodiment.

In addition, in the present embodiment, the advantageous effect of thepresent invention was explained by taking an electron beam inspectionapparatus as an example; however, the similar advantageous effect of thepresent invention can also be obtained in various apparatuses such as alength measurement SEM that measures the size of a pattern formed on thesample, an inspection apparatus that checks the existence ornonexistence of defects of a pattern formed on the sample, and a reviewSEM that observes a defect of a pattern formed on the sample. Thesimilar advantageous effect can also be obtained when a SIM observationis performed by transforming an ion beam generated at an ion source intomultiple beams and irradiating them on the sample.

Second Embodiment

In the first embodiment, in order to take a balance between the twoproblems of decreasing the beam diameter of the primary beam andseparately detecting the secondary beams, which are in the relationshipof trade-off, among the candidates of the beam allocations that satisfythe allowable range of the primary beam, the beam allocation with thehighest inspection speed was selected. In the present embodiment, byextending the first embodiment, not only the allocations of the primarybeam, but also many parameters are made variable. With this, aftersetting the optimum specifications for the sample, the conditionscapable of performing the inspection at the highest speed are searched.

Hereinafter, the present embodiment will be explained in detail withreference to FIG. 1.

As mentioned in the summary of invention, in the semiconductorinspection apparatus, the optimum inspection specifications changeaccording to the product class and the process of the sample, namely,wafer. Here, the specifications are determined by the resolution of animage formed by detected signals, the energy and current density of theprimary beam when it enters on the sample, and the specificationparameter such as the electric field intensity on the sample surface.Hereinafter, these parameters, which directly determine the advantageouseffect, are referred to as specification parameters.

These specification parameters have the following relationship with thecontrol system parameters such as the accelerating voltage (an electricpotential difference between the cathode 101 and the anode 104), theretarding voltage applied to the sample 116, a voltage applied to thesurface electric field control electrode 115, the focal lengths of thevarious lenses (the electromagnetic lens 103, the collimator lens 106,the lens array 110, the objective lenses 112 a and 112 b), the opticalsystem parameters such as the scan width of the primary beam on thesample 116, the frequency of the clock signals that the system controlsection 126 generates, the pixel size of the image formed by thedetected signals, and the stage moving speed.

The resolution of the image formed by the detected signals is determinedby the beam diameter of the primary beam to scan on the sample, thepixel size of the image that is formed based on the signals of thedetected secondary beam, and the S/N ratio of the detected signals.

The beam diameter of the primary beam is determined not only by the sizeof the cathode image 105, which is determined by the operationconditions of the electron gun constructed from the anode 104 and theelectromagnetic lens 103, but also by the focal lengths and theretarding voltages of the various lenses (the electromagnetic lens 103,the collimator lens 106, the lens array 110, the objective lenses 112 aand 112 b), and the optical magnification that is determined by thevoltage applied to the surface electric field control electrode 115, andfurthermore by the aberrations generated in each optical element and theamount of the beam blurring owing to the Coulomb repulsive force.Therefore, the beam diameter of the primary beam is also related withother conditions such as the distance of the primary beam from thecentral axis, the scan width of the primary beam on the sample 116, andthe current and the aperture angle of the primary beam.

The pixel size is the value of the scan width of the primary beam on thesample 116 divided by the number of pixels per one scan. The S/N ratiois determined by the energy of the incident primary beam on the sampleand the kind of the film composing the sample surface, which determinethe yield (the ratio of the amount of the generated secondary beam tothe amount of the incident primary beam), the current density and thepixel size of the primary beam, the scan speed, the degree ofseparability of the secondary beams, and other conditions.

The energy of the incident primary beam on the sample is determined bythe accelerating voltage (the electric potential difference between thecathode 101 and the anode 104) and the retarding voltage applied to thesample 116.

The current density of the primary beam is determined by the beamdiameter of the primary beam as mentioned above and the current of theprimary beam.

The electric field intensity on the sample surface is determined by thepositions and shapes of the ground electrode 114 and the surfaceelectric field control electrode 115, the retarding voltage applied tothe sample 116, and the voltage applied to the surface electric fieldcontrol electrode 115.

On the other hand, the inspection speed is determined by the stagemoving speed and the pixel size. The stage moving speed is determined bythe scan width, scan speed, and the settling time of the deflectionsignal that is given from the scan signal generation circuit 129 to thedeflector 113.

As mentioned above, the specification parameters and the inspectionspeed are determined by the many optical system parameters, the controlsystem parameters and the allocation of the beams. Therefore, in orderto optimize the specification parameters according to the sample, it isnecessary to adjust the combination of the above-mentioned opticalparameters and the control system parameters; however, in some samples,when the optical parameters and the control system parameters areadjusted, the electromagnetic field distribution along the passage ofthe secondary beam changes, so the distribution of the secondary beamson the detector might change, resulting in decreasing the degree ofseparability of the secondary beams. In other words, the fraction of thesecondary beams that do not enter the predetermined detector but enterother detectors or do not enter any detector might increase.

The relationship of the degree of separability of the secondary beams,optical parameter, and the allocation of the beams will be explained indetail by taking the inspection of electrical defects as an example.Because the electrical defects such as a contact failure, a wiringshort-circuit, and a void can not seen on the surface, in order todetect these defects, an inspection method to charge up the film on thesample surface by irradiating electrons and to obtain the contrast ofthe image is effective. As mentioned above, the method to charge up thesample before the inspection or measurement is referred to asprecharging. In order to enhance the advantageous effect of thisprecharging, during the inspection, when the primary beam scans on thesample, it is effective to sufficiently decrease the electric fieldintensity on the sample surface, and to increase the holding time of thecharge accumulated by the precharging. However, because the electricfield on the sample surface has an action to align the travelingdirections of the secondary beams, decreasing the electric fieldintensity on the sample surface adversely affects the performance of theinspection from the standpoint of the separation detection of thesecondary beams, so even if the secondary beam axis adjustment aligner121 and the secondary beam condenser lens 122 are adjusted, the degreeof separability of the secondary beams might decrease. Therefore, evenwhen 9 primary beams can be formed by 9 openings as shown in FIG. 2A, ifthe primary beams on the sample take the allocation C or D as shown inFIG. 2D or FIG. 2E, the degree of separability of the secondary beamsbecomes low, and in some cases, the apparatus might not be able todetect the secondary beams with a sufficient S/N ratio. In such cases,to separate the secondary beams sufficiently, it might becomeadvantageous to reduce the number of the primary beams and to broadenthe interval of the primary beams on the sample. That is, the allocationB might become more advantageous. And, during the inspection, when it isnecessary to reduce the electric field intensity on the sample surfacefurthermore, it might become more advantageous to reduce the number ofthe primary beams to one as in the allocation A.

Furthermore, in another example, when the film to form a pattern on thewafer is thin or other similar occasions, in order to increase thefraction of the primary beams to stop within the film, in some cases, itmight be more effective to sufficiently decrease the energy of theprimary beam to irradiate the sample for enhancing the sensitivity indetecting defects. However, if the energy of the primary beam isdecreased, the beam diameter of the primary beam might become largeowing to the chromatic aberration and the Coulomb repulsive force. Inaddition, in order to decrease the energy of the primary beam, when theretarding voltage applied to the sample 116 is adjusted, andfurthermore, the focal length of each lens is adjusted according to thisadjustment, the electromagnetic field distribution along the passage ofthe secondary beam might change. If this change is large, even theadjustments of the secondary beam axis adjustment aligner 121 and thesecondary beam condenser lens 122 might not be able to fully correct thetrajectory of the secondary beam, resulting in decreasing the degree ofseparability of the secondary beams. Therefore, as in the example of theinspection of electrical defects, in some cases, it might becomenecessary to reduce the number of the primary beams and to broaden theinterval of the primary beams on the sample.

As another method to prevent the secondary beams from decreasing thedegree of separability is to provide apertures to limit the intakeangles of the secondary beams in the optical system of the secondarybeams, that is, at any positions from the Wien filter 111 to thedetectors 123 d and 123 f, and to prevent the secondary beams from beingdetected other than the predetermined detectors. However, this methodnot only decreases the noise of the detected signals, but also decreasesthe amount of signals themselves, so this method is not necessarilyeffective.

Consequently, in the present embodiment, the combination of the opticalparameters, the control system parameters, and the beam allocations areoptimized so that the apparatus can achieve a good balance between theoptimum specifications for the inspection of the sample and the degreeof separability of the secondary beams to obtain the sufficient S/Nratio, and furthermore can carry out the inspection at high speed.

The procedure for carrying out the inspection in the present embodimentwill be explained in detail with reference to the flowchart shown inFIG. 5. When the operator click the Start button displayed on the imagedisplay unit 131 (step 501), the input window is displayed to specify acassette (not shown in the figure) in which a wafer to inspect isstored. When the operator input the cassette number (step 502), thewafer ID input window is displayed. The operator inputs the lot ID andthe wafer ID to which the wafer to inspect belongs (step 503). Based onthese IDs, the system control section 126 judges the wafer size andother information about the wafer, and mounts the wafer on the stage 117using the wafer loader (not shown in the figure) (step 504).

In step 505, the system control section 126 downloads the information ofthe wafer to inspect such as the product class, the process, thematerial and the thickness of the film to form on the pattern, thepattern shape, and the pattern size (design size) from the server forfactory administration based on the wafer ID. Or, the operator may inputthis information through the wafer information input window displayed onthe image display unit 131.

In step 506, the operator specifies the defect class through the Defectclass specification window displayed on the image display unit 131. Or,the system control section 126 may automatically select the defect classbased on the wafer information obtained in step 505. Here, specifyingthe defect class represents selecting whether the defect to detect is anelectrical defect (such as a contact failure, a wiring short-circuit,and a void), a shape defect (such as a crack and a protrusion indefective bore), or a foreign substance.

In step 507, the system control section 126 determines the allowablerange of the specification parameters based on the wafer informationobtained in step 505 and the defect class selected in step 505. Here,the specification parameters directly determine the advantageous effectof the inspection, and in this embodiment, they represent the resolutionof the image formed by the detected signals, the energy and the currentdensity of the incident primary beam on the sample, and the electricfield intensity on the sample surface.

In step 508, the system control section 126 calculates the value ofevery specification parameter and the estimated inspection speed for allthe combinations of the optical parameters, the control parameters, andthe beam allocations referring to a formula that has been memorizedbeforehand in the memory area inside the system control section, orreferring to a table that has been memorized beforehand in the memoryarea inside the system control section. On this occasion, the degree ofseparability of the secondary electron beams is calculated based on thebeam allocation, and based on the calculated result, the resolution iscalculated. The value of every specification parameter and the predictedvalue of the inspection speed that are obtained from the calculation arestored in the memory area inside the system control section 126.

In step 509, the system control section 126 judges whether or not theeach specification parameter calculated in step 508 satisfies theallowable conditions that were determined in step 507 for all thecombinations of the optical parameters, the control parameters, and thebeam allocations, and excludes the combinations that do not satisfy theallowable range.

In step 510, the system control section 126 selects the combination withthe highest inspection speed among the combinations that were notexcluded in step 509. With this, the combination of the opticalparameters, the control parameters, and the beam allocation isdetermined. The selected parameters and the beam allocation are storedin the system control section 126 as the log data. In addition they maybe displayed on the image display unit 131.

In step 511, in order to actualize the combination of the opticalparameters and the control parameters, the system control section 126inputs the optical parameters and the control parameters that areselected in step 509 to the optical system control circuit 127, thestage control circuit 130, the arithmetic section 126 b of the systemcontrol section 126, and the scan signal generation circuit 129. Also,the system control section 126 inputs the beam allocation selected instep 509 to the selection stage control circuit 128. With this, only thepredetermined beams among the primary beams formed by the aperture arrayenter the optical system in the downstream side.

In step 512, optical adjustment is performed for the primary beams thatentered in the optical system in the downstream side in step 511. Byusing the reference sample 132, the Faraday cup 133, and other devicesthat are mounted on the stage 117, the property of the primary beam suchas the beam diameter and current are measured for each one of the Nprimary beams selected in step 511, and whether or not they become thedesired values is confirmed. In addition, if the primary beam isestimated to be shifted for the electron optical system, the shift iscorrected using the aligner (not shown in the figure). Furthermore, ifthe settings of the accelerating voltage (the electric potentialdifference between the cathode 101 and the anode 104) and the retardingvoltage applied to the sample 116 were change in step 511, the operationconditions of the Wien filter is adjusted so that the primary beams gostraight and the secondary beams are deflected to the direction of thedetectors. After adjusting the optical system, the measurement resultsof the beam diameters and the currents before and after the correctionare displayed on the image display unit 131 for the N primary beams.FIG. 6 shows an example of a display window for the measurement resultsafter the correction. In this example, the beam allocation that thesystem control section 126 determined in step 510 is displayed in thebeam allocation display area 601, and the inspection speed that thesystem control section 126 calculated in step 508 is displayed in theinspection speed display area 602 as the estimated inspection speed.When the operator click the Measurement results tab 603, the current andthe beam diameter of the each primary beam on the sample is displayed.When the operator click the Optical parameter tab 604, every opticalparameter such as the voltage applied to the aligner that is used in thecorrection is displayed. In addition, the beam diameters and thecurrents before and after the correction, and every optical parametersuch as the voltage applied to the aligner are stored in the systemcontrol section 126 as the log data.

In step 513, the system control section 126 irradiates the primarybeams, which are entered in the optical system in the downstream side instep 511, on the sample 116 or the reference sample 132, separates thegenerated secondary beams, and adjusts the voltage (or current) appliedto the secondary beam axis adjustment aligner 121, and the focal lengthand other parameters of the secondary beam condenser lens 122 so thatthe secondary beams enter in the respective predetermined detectors.Furthermore, the system control section 126 adjusts the gain, offset,and other parameters of the amplifier circuits 124 d and 124 f, andfixes up the waveform of the signals input in the A/D converter 125.

In step 514, the specification window for the alignment is displayed onthe image display unit 131, and when the operator specifies pluralpoints in an alignment chip on the wafer through this window, theapparatus detects the alignment mark automatically, and corrects thestage coordinates for the wafer; that is, the alignment is executed.

In step 515, a trial inspection is carried out for a small region withina predetermined chip.

In step 516, the operator sets a threshold value of the image contrastto use it for judging defects based on the result of the trialinspection.

After setting the optimum threshold value, the operator clicks theInspect button displayed on the image display unit 131 to start theactual inspection (step 517). The system control section 126 memorizesthe time when the inspection is started, predicts the inspection finishtime based on the inspection speed that is calculated in step 508, anddisplays the inspection finish time on the image display unit 131.

In addition, in the present embodiment, the system control section 126calculated the value of every specification parameter and the estimatedinspection speed for all the combinations of the optical parameters, thecontrol parameters, and the beam allocations in step 508, and judgedwhether or not the each specification parameter calculated in step 508satisfies the allowable conditions for each combination; however, toreduce the processing time furthermore, the parameters may be optimizedin the order from the optical parameters or the control parameters thatstrongly affect the specification parameters to narrow down the range ofthe targets to search.

Furthermore, in the present embodiment, the system control section 126selected the combination with the highest inspection speed in step 510;however, if a judgment formula in which the inspection speed and otherspecification parameters are combined is used, the optimization of theoptical parameters, the control parameters, and the beam allocation canbe performed by weighting the specified parameters.

Or, the system control section 126 leaves plural combinations as thecandidates of the combinations in step 511, and the operator maydetermine the final optical parameters, control parameters, and the beamallocation using the image obtained from the trial inspection in step516. Or, the operator or the system control section 126 may determinethe final optical parameters, control parameters, and the beamallocation by selecting a combination that separates the differencebetween the normally formed pattern and the poorly formed pattern moreeffectively using the histogram of the brightness of every pixel of theimage

1. A charged particle beam apparatus having a function to inspect ormeasure a sample by generating a charged particle beam by unit of asingle charged particle beam source, separating the charged particlebeam into a plurality of primary beams, irradiating the primary beams onthe sample, detecting generated secondary beams, and processing thedetected signals that are obtained thereof, the charged particle beamapparatus comprising: a primary optical system, wherein it forms theplurality of primary beams to scan on the sample; a secondary opticalsystem, wherein it separately detects the secondary beams generated byirradiating the plurality of primary beams on the sample; and a controlunit of the charged particle beam apparatus, wherein the control unitoperates the primary optical system so that it selects at least a partof the plurality of primary beams to scan on the sample according to theproperty of the sample.
 2. The charged particle beam apparatus accordingto claim 1, wherein the control unit calculates the detectionresolution, inspection speed, or measurement speed of the secondarybeams corresponding to the number and allocation of the primary beams toreach the sample, and selects the optimum allocation in which theinspection speed or measurement speed becomes highest among theallocations that satisfy the detection resolution necessary to carry outthe inspection or measurement of the sample.
 3. The charged particlebeam apparatus according to claim 1, wherein the primary optical systemincludes a unit enabling any one or more beam among the plurality ofprimary beams to reach the sample.
 4. The charged particle beamapparatus according to claim 1, further comprising: an image processingunit to form image information on the scan area from the detectedsignals.
 5. The charged particle beam apparatus according to claim 1,further comprising: a sample table to mount the sample; and a samplestage to move the sample table to any position for the irradiationposition of the primary beam, wherein the control unit determines themoving speed of the sample stage based on the property of the sample. 6.The charged particle beam apparatus according to claim 1, wherein theprimary optical system includes: a first lens to focus the plurality ofprimary beams on the sample; a unit to apply a retarding electricpotential to the sample table; an electrode to adjust the electric fieldintensity on the sample surface; and a scanning deflector to scan theplurality of the primary beams on the sample, wherein the control unitchanges any of the focal length of the first lens, the voltage appliedto the electrode, the voltage applied to the sample, the scan width forthe charged particle beam of the scanning deflector or the scanningspeed of the deflector according to the property of the sample.
 7. Thecharged particle beam apparatus according to claim 4, wherein thesecondary optical system includes: a detector for the secondary beamgenerated from the irradiation of the primary beam; and a secondary beamtransfer system to lead the secondary beam to the detector, and whereinthe control unit determines any of the frequency of a clock signal thatdetermines the timing for detecting signals or the pixel size of theimage, according to the property of the sample.
 8. The charged particlebeam apparatus according to claim 7, wherein the secondary opticalsystem includes: a secondary lens or an aligner; and an adjustment unitof the secondary lens or the aligner, and wherein the secondary opticalsystem includes a unit to adjust the secondary lens or the aligner toseparately detect the secondary charged particles, which are generatedfrom the sample by irradiating the extracted charged particle beamsusing the extraction unit, by unit of the detection system.
 9. Thecharged particle beam apparatus according to claim 5, wherein any of theproduct class, the process, the material of film to form a pattern, thethickness of the film to form the pattern, the shape of the pattern, andthe size of the pattern is used as the property of the sample.
 10. Thecharged particle beam apparatus according to claim 1, furthercomprising: a measurement unit to measure the beam diameter of theprimary beam that reaches on the sample and the beam current; and a unitto adjust the current of the primary beam based on the measurementresult of the measurement unit.